1. Field of the Invention
This invention relates to chemical sensors. More specifically, the invention is a wireless chemical sensor that includes a material whose electrical conductivity changes in the presence of a chemical of interest, where such electrical conductivity changes a harmonic response of a spaced-apart electrically-unconnected geometric pattern that is electrically conductive.
2. Description of the Related Art
Chemical sensors have been employed for a large variety of applications such as bio-sensing, environmental analysis, food analysis, clinical diagnostics, drug detection, gas detection, toxicity detection, and detection of chemicals that could be used for warfare or terrorism. In one approach, sensors have a specific synthesized receptor that selectively binds with an analyte of interest. Another sensor approach is to have a specific chemical reactant react with a target reactant. Each approach produces a measurable change that is discernable via an electrical component such as a capacitor or resistor. Typically, the receptor/reactant must physically contact some part(s) of the electrical component(s). This can limit the number of applications that could utilize chemical sensors.
Chemical sensor innovation is driven by either the infrastructure innovations such as microelectromechanical or wireless sensors, or innovations/discoveries in chemistry such as the development of Carbon-60 that resulted in carbon nanotubes and the development of conductive polymers. Newer sensor baseline circuit designs include magnetic field response sensors that require no physical connections to a power source or acquisition hardware. For example, U.S. Pat. Nos. 7,086,593 and 7,159,774 disclose magnetic field response sensors designed as passive inductor-capacitor circuits and passive inductor-capacitor-resistor circuits that produce magnetic field responses whose harmonic frequencies correspond to states of physical properties of interest. A closed-circuit magnetic field response sensor is made by electrically connecting a spiral trace inductor to an interdigitated electrode capacitor or capacitor plates. A magnetic field response recorder wirelessly transmits a time-varying magnetic field that powers each sensor using Faraday induction. Each sensor then electrically oscillates at a resonant frequency that is dependent upon the capacitance, inductance and resistance of each sensor. The frequency, amplitude and bandwidth of this oscillation are wirelessly sensed by the magnetic field response recorder. The sensor's response is indicative of a parameter that is to be measured.
While the above-described magnetic field response measurement acquisition system greatly improves the state-of-the-art of wireless sensing, electrical connections are still required between the sensor's inductor and capacitor. Such connections are subject to breakage, especially if the sensor will undergo flexing during its useful life.